The behavior of impurity ions in the p-pentyl-p′-cyano-biphenyl liquid crystal cell were investigated by evaluating the low-frequency dielectric dispersion characteristic of the liquid crystal cell. The dependence of the behavior of the impurity ions on the presence of polyimide LB film was also investigated. It was found that in a liquid crystal cell without an LB layer, an electric double layer was formed, and that in a cell with an LB layer, interfacial polarization was present between the liquid crystal layer and LB layer. It was also found that in a liquid crystal cell with ultrathin LB films, the characteristics of the cell strongly depended on the number of LB layers. © 1997 Scripta Technica, Inc. Electron Comm Jpn Pt 2, 80(5): 40–46, 1997